Switchgear load sharing for oil field equipment

ABSTRACT

A hydraulic fracturing system for fracturing a subterranean formation is disclosed. In an embodiment, the system may include a plurality of electric pumps fluidly connected to a well associated with the subterranean formation and powered by at least one electric motor, and configured to pump fluid into a wellbore associated with the well at a high pressure so that the fluid passes from the wellbore into the subterranean formation and fractures the subterranean formation; at least one generator electrically coupled to the plurality of electric pumps so as to generate electricity for use by the plurality of electric pumps; and at least one switchgear electrically coupled to the at least one generator and configured to distribute an electrical load between the plurality of electric pumps and the at least one generator.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.15/893,766, filed Feb. 12, 2018, now U.S. Pat. No. 10,686,301 issuedJun. 16, 2020, which is a continuation of U.S. application Ser. No.15/487,694, filed Apr. 14, 2017, now U.S. Pat. No. 9,893,500 issued Feb.13, 2018, and claims priority to and the benefit of U.S. ProvisionalApplication Ser. No. 62/323,168, filed Apr. 15, 2016, and is acontinuation-in-part of, and claims priority to and the benefit of, U.S.application Ser. No. 15/235,788, filed Aug. 12, 2016, which is in turn acontinuation-in-part of, and claims priority to and the benefit of, U.S.application Ser. No. 15/202,085, filed Jul. 5, 2016, now U.S. Pat. No.10,337,308 issued Jul. 2, 2019, which is a continuation of, and claimspriority to and the benefit of, U.S. application Ser. No. 13/679,689filed Nov. 16, 2012, now U.S. Pat. No. 9,410,410, issued Aug. 9, 2016,and is further a continuation-in-part of, and claims priority to and thebenefit of, U.S. application Ser. No. 15/145,491, filed on May 3, 2016,now U.S. Pat. No. 10,036,238 issued Jul. 31, 2018, which is acontinuation-in-part of, and claims priority to and the benefit of, U.S.application Ser. No. 13/679,689 filed Nov. 16, 2012, now U.S. Pat. No.9,410,410, issued Aug. 9, 2016, the full disclosures of which are herebyincorporated by reference herein for all purposes.

BACKGROUND 1. Technical Field

This disclosure relates generally to hydraulic fracturing and moreparticularly to systems and methods for spare turbine power generation,which is sometimes referred to as reserve power.

2. Background

With advancements in technology over the past few decades, the abilityto reach unconventional sources of hydrocarbons has tremendouslyincreased. Horizontal drilling and hydraulic fracturing are two suchways that new developments in technology have led to hydrocarbonproduction from previously unreachable shale formations. Hydraulicfracturing (fracturing) operations typically require powering numerouscomponents in order to recover oil and gas resources from the ground.For example, hydraulic fracturing usually includes pumps that injectfracturing fluid down the wellbore, blenders that mix proppant into thefluid, cranes, wireline units, and many other components that all mustperform different functions to carry out fracturing operations.

Usually in fracturing systems the fracturing equipment runs ondiesel-generated mechanical power or by other internal combustionengines. Such engines may be very powerful, but have certaindisadvantages. Diesel is more expensive, is less environmentallyfriendly, less safe, and heavier to transport than natural gas. Forexample, heavy diesel engines may require the use of a large amount ofheavy equipment, including trailers and trucks, to transport the enginesto and from a wellsite. In addition, such engines are not clean,generating large amounts of exhaust and pollutants that may causeenvironmental hazards, and are extremely loud, among other problems.Onsite refueling, especially during operations, presents increased risksof fuel leaks, fires, and other accidents. The large amounts of dieselfuel needed to power traditional fracturing operations requires constanttransportation and delivery by diesel tankers onto the well site,resulting in significant carbon dioxide emissions.

Some systems have tried to eliminate partial reliance on diesel bycreating bi-fuel systems. These systems blend natural gas and diesel,but have not been very successful. It is thus desirable that a naturalgas powered fracturing system be used in order to improve safety, savecosts, and provide benefits to the environment over diesel poweredsystems. Turbine use is well known as a power source, but is nottypically employed for powering fracturing operations.

Though less expensive to operate, safer, and more environmentallyfriendly, turbine generators come with their own limitations anddifficulties as well. As is well known, turbines generally operate moreefficiently at higher loads. Many power plants or industrial plantssteadily operate turbines at 98% to 99% of their maximum potential toachieve the greatest efficiency and maintain this level of use withoutsignificant difficulty. This is due in part to these plants having asteady power demand that either does not fluctuate (i.e., constant powerdemand), or having sufficient warning if a load will change (e.g., whenshutting down or starting up a factory process).

In hydraulic fracturing, by contrast, the electrical load constantlychanges and can be unpredictable. This unpredictability is due to theprocess of pumping fluid down a wellbore, which can cause wellheadpressure to spike several thousand PSI without warning, or can causepressure to drop several PSI unexpectedly (sometimes called a “break,”as in the formation broke open somewhere). In order to maintain aconsistent pump rate, the pump motors are required to “throttle” up or“throttle” down (applying more or less torque from a variable frequencydrive), drawing either more or less electrical power from the turbineswith little to no notice in many situations.

Concurrently with pressure variations, fluid rate variations can alsooccur. At any moment, the contracting customer may ask for an extra 5barrels per minute (bpm) of pump rate or may request an instantlydecreased pump rate with little to no warning. These power demandchanges can vary from second to second—unlike industrial power demands,which may vary from hour to hour or day to day, allowing for planningand coordination.

Hydraulic horsepower (HHP) can be calculated with the followingrelationship:

${HHP} = \frac{\left( {{Wellhead}\mspace{14mu}{Pressure}} \right) \times \left( {{Pump}\mspace{14mu}{Rate}} \right)}{40.8}$HHP also directly correlates with the power demand from the turbines,where:HHP≈Electrical Power DemandTherefore, if both variables (rate and pressure) are constantlychanging, maintaining a steady power demand can be difficult. Due tothis, it is impossible to design the equipment and hold the turbineoutput at 98%-99% of full potential because a minute increase in powerdemand may shut the turbines down and may result in failure of thefracturing job. To prevent such turbine shutdown from happening,fracturing equipment is designed to only require approximately 70% ofthe maximum output of the turbine generators during normal and expectedoperating conditions. This allows the fleet to be able to operateagainst changing fracturing conditions, including increased fluid rateand increased wellhead pressure.

There are also other small loads which contribute to changing powerdemand. These include turning on or off small electrical motors forhydraulic pumps, chemical pumps, cooling fans, valve actuators, smallfluid pumps, etc., or power for metering instrumentation, communicationequipment, and other small electronics. Even lighting or heating cancontribute to the fluctuating power load.

Therefore it may be desirable to devise a means by which turbine powergeneration can be managed at an output usable by fracturing equipment.

SUMMARY

The present disclosure is directed to a method and system for providingelectrical load sharing between switchgear trailers acting as power hubsto combine the output of multiple electrical generators.

In accordance with an aspect of the disclosed subject matter, the methodand system of the present disclosure provide a hydraulic fracturingsystem for fracturing a subterranean formation. In an embodiment, thesystem can include a plurality of electric pumps fluidly connected tothe formation and configured to pump fluid into a wellbore at highpressure so that the fluid passes from the wellbore into the formationand fractures the formation; at least one generator electrically coupledto the plurality of electric pumps so as to generate electricity for useby the plurality of electric pumps; and at least one switchgearelectrically coupled to the at least one generator and configured todistribute an electrical load between the plurality of electric pumpsand the at least one generator.

In an embodiment, the system including the plurality of electric pumps,the at least one generator, and the at least one switchgear can be asingle electrical microgrid.

In an embodiment, the system making up the single electrical microgridcan be split into two or more electrical banks. In an embodiment, eachof the two or more electrical banks can include at least one generatorand at least one switchgear. In an embodiment, when one or more of thetwo or more electrical banks is shut down, each of the other activeelectrical banks can be configured to distribute the electrical loadbetween the plurality of electric pumps and the at least one generatorassociated with each active electrical bank.

In an embodiment, the system can further include at least two switchgearunits electrically coupled to the at least one generator, and a tiebreaker electrically coupled between each of the at least two switchgearunits.

In an embodiment, the tie breaker can be configured to evenly distributethe electrical load between the plurality of electric pumps and the atleast one generator when the tie breaker is in a closed position; andisolate one or more of the plurality of electric pumps, the at least onegenerator, and the at least two switchgear units when the tie breaker isin an open position.

In an embodiment, when the tie breaker is in the closed position, atleast one generator is shut down and at least one other generator isactive, the electrical load can be evenly distributed among the at leastone other active generators.

In an embodiment, the tie breaker can include a long distancetransmission line.

In an embodiment, the at least one switchgear can be configured todistribute power among any of one or more transformers, auxiliaries, orother switchgear units, or a combination thereof.

In an embodiment, the one or more auxiliaries can include any of ablender, electric wireline equipment, a water transfer pump, an electriccrane, a data van, a work trailer, living quarters, an emergency shower,sand equipment, a turbine inlet chiller, a compressor station, a pumpingstation, a second fracturing site, a drill rig, or a nitrogen plant, ora combination thereof.

In an embodiment, the at least one generator can be one of a turbinegenerator or a diesel generator, or a combination thereof.

In an embodiment, the at least one turbine generator can be powered bynatural gas.

In an embodiment, wherein each component of the system can be modularand movable to different locations on mobile platforms.

In an embodiment, the system can further include a power connectionpanel associated with the plurality of electric pumps. In an embodiment,the power connection panel can include a plurality of power connectionsfor each of the plurality of electric pumps, and a system groundconnection configured to act as a ground between the plurality ofelectric pumps and a transformer. In an embodiment, the transformer canbe configured to provide power to the plurality of electric pumps.

In an embodiment, the system can further include a variable frequencydrive connected to the at least one electric motor to control the speedof the at least one electric motor. In an embodiment, the variablefrequency drive can frequently perform electric motor diagnostics toprevent damage to the at least one electric motor.

In accordance with another aspect of the disclosed subject matter, themethod and system of the present disclosure provide a hydraulicfracturing system for fracturing a subterranean formation. In anembodiment, the system can include a plurality of electric pumps fluidlyconnected to the formation and configured to pump fluid into a wellboreat high pressure so that the fluid passes from the wellbore into theformation and fractures the formation; at least one turbine generatorelectrically coupled to the plurality of electric pumps so as togenerate electricity for use by the plurality of electric pumps; atleast two switchgear units electrically coupled to the at least oneturbine generator and configured to distribute an electrical loadbetween the plurality of electric pumps and the at least one turbinegenerator; a tie breaker electrically coupled between each of the atleast two switchgear units and configured to evenly distribute theelectrical load between the plurality of electric pumps and the at leastone turbine generator when the tie breaker is in a closed position; anda variable frequency drive connected to the at least one electric motorto control the speed of the at least one electric motor, wherein thevariable frequency drive frequently performs electric motor diagnosticsto prevent damage to the at least one electric motor.

Other aspects and features of the present disclosure will becomeapparent to those of ordinary skill in the art after reading thedetailed description herein and the accompanying figures.

BRIEF DESCRIPTION OF DRAWINGS

Some of the features and benefits of the present disclosure having beenstated, others will become apparent as the description proceeds whentaken in conjunction with the accompanying drawings, in which:

FIG. 1 is a schematic example of a turbine generator in communicationwith an electronic equipment room, which connects to a switchgearaccording to an embodiment of the disclosure.

FIG. 2 is a perspective view of an example of a turbine generator andelectronic equipment room according to an embodiment of the disclosure.

FIGS. 3A and 3B are perspective views of a switchgear trailer accordingto an embodiment of the disclosure.

FIG. 4 is a perspective view of cables connecting to a hydraulicfracturing pump trailer according to an embodiment of the disclosure.

FIGS. 5-15 are block diagrams of portions of a microgrid having aplurality of turbine generator sets and switchgear units according tovarious embodiments.

While the disclosure will be described in connection with the preferredembodiments, it will be understood that it is not intended to limit thedisclosure to that embodiment. On the contrary, it is intended to coverall alternatives, modifications, and equivalents, as may be includedwithin the spirit and scope of the disclosure as defined by the appendedclaims.

DETAILED DESCRIPTION

The method and system of the present disclosure will now be describedmore fully hereinafter with reference to the accompanying drawings inwhich embodiments are shown. The method and system of the presentdisclosure may be in many different forms and should not be construed aslimited to the illustrated embodiments set forth herein; rather, theseembodiments are provided so that this disclosure will be thorough andcomplete, and will fully convey its scope to those skilled in the art.Like numbers refer to like elements throughout. In an embodiment, usageof the term “about” includes +/−5% of the cited magnitude. In anembodiment, usage of the term “substantially” includes +/−5% of thecited magnitude.

It is to be further understood that the scope of the present disclosureis not limited to the exact details of construction, operation, exactmaterials, or embodiments shown and described, as modifications andequivalents will be apparent to one skilled in the art. In the drawingsand specification, there have been disclosed illustrative embodimentsand, although specific terms are employed, they are used in a genericand descriptive sense only and not for the purpose of limitation.

Described herein is an example of a method and system for providingelectrical load sharing between switchgear trailers acting as power hubsto combine the output of multiple electrical generators. Adding a tiebreaker between two switchgear trailers can eliminate the need for athird switchgear trailer, while still retaining the ability to evenlydistribute power between all of the equipment, and to concurrentlyevenly distribute the electrical load between a plurality of turbinegenerator sets.

A feature of the switchgear configurations described herein is thecapability to selectively choose between either load sharing, to provideefficiency and flexibility; or having isolated banks of equipment, toprovide protection and redundancy. In an embodiment, the switchgearoptionally includes a tie breaker. The tie breaker can synchronizethree-phase power of a similar voltage and frequency from differentsources to act as a common bus, and can evenly distribute the electricalload between a plurality of electric pumps and turbine generators whenthe tie breaker is in a closed position. The tie breaker will isolateone or more of the plurality of electric pumps, the turbine generator,and the switchgear units when the tie breaker is in an open position.The use of a tie breaker can provide an advantage over previous loadsharing systems because use of a tie breaker provides more options forthe equipment operators and allows the fleet to be more versatile as towhich mode of operation—protection and redundancy, or efficiency andflexibility—is more desirable at any given moment.

Another favorable aspect of load sharing is the ability to shutdownturbines when peak power output is not required. If the power load isdistributed evenly between all of the generator sets in the fleet, thenit can be possible to shut down unnecessary power generation as long asthe remaining generator sets can compensate for the loss and pick up theextra load placed on them. This flexibility for partial shutdown canallow the remaining turbines to operate at a higher efficiency, whichcan reduce wear on the fleet by not running every turbine continuously,and increase efficiency while reducing emissions by allowing fewerturbines to run in a lower emissions mode. The lower emissions mode iscalled SoloNox, and can be performed due to load sharing using aswitchgear, because the turbines can only operate in this mode whileoperating above a 50% load. In some embodiments, directly poweringfracturing pumps can involve using all turbines regardless of therequired power load.

In an embodiment, a variable frequency drive (VFD)—and in some cases, anA/C console used to keep the VFD from overheating—can be utilized tocontrol the speed of an electric motor associated with a pump powered bythe turbine(s).

In some examples, certain tasks can be accomplished with fewer turbines.Instead of having redundancy or spare power generation available toisolated power banks, the reserve power generation capability can beconsolidated across the entire fleet. Requiring fewer turbine generatorsmeans the equipment can now fit on smaller well sites which reduces theneed to clear more land and disrupt the surrounding environment tocreate a larger pad, and reduces the costs associated with such clearingand construction.

The systems described herein are not limited to use in processesinvolving hydraulic fracturing. For example, the system includeselectric fracturing equipment and power generation equipment. The powergeneration equipment can be used to supply any oilfield equipmentincluding compressor stations, pumping stations, nitrogen plants, CO₂plants, drilling rigs, work-over rigs, barracks, coiled tubing units,refineries, or other systems or applications that do not have access toa utility provided power grid or that have a dynamic power load or lowpower factor.

FIG. 1 is a block diagram showing the basic components of a hydraulicfracturing well site power generation system 100 for providingelectrical load sharing according to an embodiment. A turbine generator105 can include a natural gas turbine engine coupled to a three-phase,60 hertz (Hz) electric generator to produce power as the turbine enginerotates. In an alternative, the generator can generate electricity at 50Hz. or at any other power level useful for hydraulic fracturing fleets.In the illustrated embodiment, the turbine generator 105 is shown beingelectrically connected to an electronic equipment room (EER) 115, whichcan house wiring, breakers, controls, monitoring systems, firesuppression support, and a battery bank for secondary power when theturbine is not operating and there is no other power source. In someexamples, the battery bank can power lighting, fire suppression,emergency turbine lube pumps, and onboard electronics. The combinationof a turbine generator 105 and an EER 115 can be referred to as agenerator set. A switchgear trailer 125 can provide power distribution,high voltage breakers, and “lock-out, tag-out” (a safety procedure usedto ensure that dangerous machines are properly shut off and not able tobe started up again prior to the completion of maintenance or servicingwork) capabilities.

Transformers can optionally be included with the equipment of FIG. 1. Asillustrated in the embodiment shown in FIG. 1, an air intake filterhouse 110 can be positioned on top of or adjacent to the turbinegenerator 105, and a catwalk 120 can connect turbine generator 105 andEER 115 for ease of access. The system 100 as a whole can define anexample of an electrical microgrid.

FIG. 2 shows a perspective view of an example system 200 having a singlegenerator set with a turbine generator 205 and an overhanging filterhouse 210 according to an embodiment. A power cable 206 can connect theturbine generator 205 to an EER 215 with plugs 204-a, 204-b. In someembodiments, plugs 204-a, 204-b are enclosed and concealed whileenergized. Between turbine 205 and EER 215 is an elevated catwalk 220with stairs leading to the EER 215 for employee access, in theillustrated embodiment. Turbine 205 can also include maintenance hatchesfor purposes of employee access. A plug 202 can provide a power cablebetween the EER 215 and a switchgear trailer (not shown).

An example 300-a of a switchgear trailer 325 is shown in an endperspective view in FIG. 3A. Electrical connections 302 for turbines andan auxiliary trailer are shown in recesses formed on a lateral surfaceof the trailer 325. A side opposite the lateral side of the trailer 325,as shown in the example 300-b according to an embodiment illustrated inFIG. 3B, can include electrical connections 302 for transformers.

FIG. 3B illustrates in side perspective view a side of the switchgeartrailer 325 opposite from that of shown in FIG. 3A. In the illustratedexample, switchgear trailer 325 can be an example of a switchgear “B”trailer. Four connections 302 are visible, which are for the 13.8 kVcable that spans between the switchgear and the transformers. Eachconnection 302 is a cable that contains all three electrical phases, aground, and a ground check; which is different from the cablingconfiguration of FIG. 4, which relies on the use of multiple conductorsper phase, as discussed below.

The switchgear trailer 325 can house large breakers and fault protectionequipment required for safe operations and for “lock-out, tag-out” ofpower going to selected equipment. The switchgear is optionally ratedfor 15 kV (13.8 kV), and can be designed or reconfigured for differentvoltages, such as 138 kV, 4.160 V. or 600 V, or any other voltagesuitable for fracturing fleet operations. The switchgear can includeground fault detection, color coordinated cable receptacles, interlocksystem, and other safety features.

Illustrated in a side perspective view in FIG. 4 is an example 400 ofmultiple single-conductor cables connecting to a fracturing pump trailer425, according to an embodiment. In the illustrated example, a 600 Vpower connection panel 401 contains power connections for two fracturingpumps. Each electrical phase is split into two separate cables. An upperrow of plugs 402-a can be used to power one fracturing pump, while alower row of plugs 402-b can be used to power a second fracturing pumpon the same fracturing pump trailer 425.

In the illustrated example, the upper row of plugs 402-a includes sixsingle-phase cable connections, and the lower row of plugs 402-bincludes six single-phase cable connections, allowing for two cables perphase. The plugs can be color-coded based on the electrical phase. Thepower connection panel 401 can also include a control power cable 404and a system ground cable 406. The system ground cable 406 can act as aground between the fracturing pump trailer 425 and a 13.8 kV to 600 Vtransformer (not shown) providing power to the fracturing pump trailer425. Additional cables can span between the 13.8 kV to 600 V transformerand the fracturing pump trailer 425.

FIG. 5 is a block diagram illustrating one example 500 of a plurality ofgenerator sets 505-a. 505-b, 505-c for use with a system for fracturinga subterranean formation. Each generator set 505-a, 505-b, 505-c caninclude a turbine engine with sufficient mechanical power to rotate anelectric generator with sufficient electrical power to provideelectricity to a small, closed circuit, electrical grid. This grid canbe considered part of the microgrid.

For the sake of discussion herein, certain types of switchgear unitshave nomenclature based on their application; for example a switchgear“A” can distribute power to other switchgear units, a switchgear “B” cantransmit power to transformers and auxiliaries, and a switchgear “C” cantransmit power to transformers. However, a switchgear trailer is notlimited to the previously stated configurations. It is possible to powermore than four transformers from a switchgear “B” or switchgear “C”; anda switchgear “B” can supply more than one auxiliary trailer if needed.Similarly, a switchgear “A” is not limited to connections for only threeor four generator sets and only two switchgear trailers. The denotationof A, B, C, A+, B+ and C+ switchgear units does not reflect industrystandards, but is a naming convention for use herein.

In the illustrated embodiment, switchgear “A” 525-a is an electrical hubcombining the power output of three 5.7 MW natural gas turbinegenerators from generator sets 505-a, 505-b, 505-c. Further in thisexample, switchgear “A” 525-a can supply electrical power to two otherswitchgear units. Switchgear “B” 525-b can receive power from switchgear“A” 525-a and distribute the power to an auxiliary unit and multipletransformers, as shown. Switchgear “C” 525-c can also receive power fromswitchgear “A” 525-a and distribute the power to one or moretransformers, but in the illustrated embodiment does not distributepower to an auxiliary unit.

In this example, the illustrated lines leading between the generatorsets 505-a, 505-b, 505-c, switchgear units 525-a, 525-b, 525-c, andauxiliary units and transformers can be 13,800 volt, three-phase, 60 Hz,power lines. This example allows load distribution between all threeturbines in generator sets 505-a, 505-b, 505-c through switchgear “A”525-a. Optionally, the power demand placed on each generator set 505-a.505-b, 505-c can be equal, and each generator set 505-a, 505-b, 505-ccan run at an equal output.

FIG. 6 is a block diagram showing an embodiment 600 illustrating aplurality of generator sets 605-a, 605-b, 605-c for use with a systemfor fracturing a subterranean formation. Similarly to the example 500illustrated in FIG. 5, switchgear “A” 625-a is an electrical hubcombining the power output of three 5.7 MW natural gas turbinegenerators from generator sets 605-a, 605-b. 605-c, where switchgear “A”625-a can supply electrical power to two other switchgear “B” units625-b-1, 625-b-2. While described as being a 5.7 MW generator, othergenerator configurations capable of operating at other power outputs arealso envisioned. For example, in an embodiment, a 6.5 MW turbinegenerator can be used.

In contrast to the example provided in FIG. 5, in this exampleswitchgear “C” 525-c is replaced with a second switchgear “B” 625-b-2.Both switchgear “B” units 625-b-1, 625-b-2 couple to and provide powerfor a secondary auxiliary, which can include any one or more of asecondary blender, electric wireline, water transfer, crane, a seconddata van, turbine inlet chillers, and the like.

FIG. 7 is a block diagram of another example 700 of a switchgear layoutfor use with a fracturing system, according to an embodiment. In thisexample, switchgear “A” 625-a of FIG. 6 is substituted with switchgear“A+” 725-a, allowing for connections and breakers for a fourth generatorset 705-d. This configuration allows for powering more equipment for awider range of applications. Switchgear “A+” 725-a can supply electricalpower to two other switchgear “B” units 725-b-1, 725-b-2. In analternate embodiment, one or more of switchgear “B” units 725-b-1,725-b-2 can be replaced with a switchgear “B+” unit. This embodimentprovides advantages with regard to cost, as existing switchgear trailerscan be upgraded or modified accordingly without the need for purchasingnew trailers.

FIG. 8 is a block diagram illustrating an alternate example 800 of aplurality of generator sets for use with a system for fracturing asubterranean formation, according to an embodiment. In the illustratedexample, the power transmission network is broken into two banks withdirect communication between generator sets 805-a, 805-b and switchgear“B” 825-b-1 in the first bank 807-a, and generator sets 805-c, 805-d andswitchgear “B” 825-b-2 in the second bank 807-b. Generator sets 805-a,805-b can be load sharing through one switchgear “B” 825-b-1, andgenerator sets 805-c, 805-d can be load sharing through anotherswitchgear “B” 825-b-2. Direct communication between generator sets805-a, 805-b, 805-c, 805-d and switchgear “B” 825-b-1, 825-b-2 canrequire fewer switchgear trailers, which can save space, decreaseequipment costs, and decrease the amount of cables being run, whileallowing addition of a fourth generator set 805-d.

Splitting the microgrid into two banks 807-a, 807-b can build redundancyinto the system. If a single generator set fails during peak powerdemand, any other generator set on the same circuit can share the load.If the load is too high, the other turbines will shut down, causing acomplete blackout; in hydraulic fracturing, this can result in a “screenout.” During a “screen out,” the fluid in the wellbore is full of sandwhen the pumps stop, causing the sand to drop out of suspension in thefluid and plug off the well, which is expensive and time consuming toclean out. With two separate electrical banks, a failure in one bank(due to a ground fault, mechanical breakdown, software issue, fuelproblem, cable issue, breaker failure, etc.) will not cause a failure inthe other bank. The load on the opposite pair of turbines will remainthe same, resulting in only a blackout for half of the equipment;operators can flush the well bore with half of the equipment in mostsituations. Two switchgear units “B” can be used to allow either bank toprovide power to a blender, which allows the hydraulic fracturingequipment that is connected to either power bank to be self-sufficientand capable of flushing the well bore in event of a generator failure.

In the example of FIG. 8, if all four turbines 805-a. 805-b, 805-c,805-d were operating at 50% while configured in pairs on two separatepower banks 807-a, 807-b, shutting one turbine down in a given load bankwill result in the other turbine in that pair having to pick up theentire power demand for the bank (circuit). This will result in 100%load on a single turbine, and could likely shut down the operatingturbine, causing a blackout for half of the equipment. In the summermonths when temperatures are elevated, turbine engines cannot reachtheir maximum potential as power output is derated due to the hotambient air being less dense. Thus all four turbines may be required tooperate despite their load percentage being as low as 35% in certaincases.

Another alternate example 900 of a plurality of generator sets for usewith a system for fracturing a subterranean formation is schematicallyillustrated in FIG. 9. Similarly to the example 800 illustrated in FIG.8, generator sets 905-a, 905-b and switchgear “B+” 925-b-1 can make up afirst bank 907-a, and generator sets 905-c, 905-d and switchgear “B+”925-b-2 can make up a second bank 907-b. Differently from example 800,however, in the illustrated example 900, the switchgear units 925-b-1,925-b-2 are able to load share with one another.

Example cables are shown spanning between the two “B+” switchgear units925-b-1, 925-b-2, which optionally are 13.8 kV cables for a tie breaker909. Tie breaker 909 can allow for complete load sharing between allfour turbines in generator sets 905-a, 905-b, 905-c, 905-d without theneed for a switchgear “A,” as illustrated in FIG. 5. A bus tie breaker909 between switchgear “B+” 925-b-1 and switchgear “B+” 925-b-2 can beused when combining the power output from difference sources, such as inthe case of using multiple generator sets 905-a, 905-b, 905-c, 905-d.

In one example of operation of the system of FIG. 9, all four turbines905-a, 905-b, 905-c, 905-d can continue to operate even at loads below50%, which can increase fuel consumption and wear on the turbines. Forexample, if four load sharing turbines were operating at a 50% load, oneturbine could be shut down, allowing the other turbines to distributethe power demand, resulting in three turbines running at approximately67% load. Turbines typically operate more efficiently at higher loadsand the turbine generators enter the lean dry fuel ratio mode at above50% load, allowing them to operate at higher efficiency with loweremissions than normal.

In one example procedure for starting the turbine generators, allbreakers (not shown) in each switchgear and EER can be set to an openposition such that no electricity passes across the breakers, andgenerator set 905-b can be started from a black start generator (notshown). Once generator set 905-b is running and operating steadily,generator set 905-b can be connected to the bus on switchgear “B+”925-b-1 by closing the breakers in each switchgear and EER.

In the described embodiment, generator set 905-a can be started throughthe power supplied from switchgear “B+” 925-b-1, which can in turn bepowered by generator set 905-b. This configuration is commonly known asback-feeding, a process that ensures that the generators are in syncwith each other. Operating out of sync, operating with three electricalphases not having identical phase angles, or operating when any twophases are reversed, can each cause catastrophic damage to the system.

Phase synchronization can be controlled by the EER, and may not allowcurrent to flow onto a common power bus between two electrical sources(by keeping breakers open in the EER) until synchronization is complete.A tie breaker can also be used to synchronize the electrical phases sothat two separate generator sources can be put on a bus together toprovide power to equipment. In some cases, the electrical sources can bethe two isolated switchgear units 925-b-1, 925-b-2.

A tie breaker can be installed in each switchgear “B+” 925-b-1, 925-b-2to allow generator sets 905-a, 905-b, 905-c, 905-d to be synchronizedand placed on a single bus together. Thus the two switchgear units “B+”925-b-1, 925-b-2 can act as a single switchgear to provide load sharing,power transmission, and breaker protection to all four generator sets905-a. 905-b, 905-c, 905-d. If load sharing is desired, the tie breakercan be used to close the joining breaker 909 between the switchgear “B+”925-b-1, 925-b-2 trailers, which can allow for electrical current toflow in either direction to balance the load. If having two separateelectrical banks 907-a, 907-b is desired, the joining breaker 909 can bekept open, separating the switchgear units “B+” 925-b-1, 925-b-2 fromeach other electrically.

This switchgear model example 900 can provide an option to have modulargenerator sets 905-a, 905-b. 905-c, 905-d. If only two or threegenerator sets are required, for example due to ambient temperatures orcustomer requirements, one or more generator sets can be shut down (ornot rigged in). In the described configuration, even with one or moregenerator sets shut down, the system can nevertheless balance the loadproperly to supply power to the equipment, and to run the remainingturbines at a higher load and efficiency. During startup, the turbinegenerators can be started by back-feeding from the common bus 909 of theswitchgear units “B+” 925-b-1, 925-b-2, as long as one turbine generatoris started from the black start generator (not shown).

FIG. 10 is a block diagram illustrating an example 1000 of a portion ofa power flow diagram of a microgrid for use with a wellbore fracturingsystem, which includes electrical connections for 480 V, 600 V, and 13.8kV, according to an embodiment. Shown are gas compressors 1030-a,1030-b, which can be powered by electricity in some examples, but canoptionally be powered by combusting fuel, such as natural gas, diesel,and the like, in other examples. Fuel gas filtration and heating units1035-a, 1035-b, 1035-c, 1035-d are also depicted.

A black start generator 1003 is shown in electrical communication withgenerator sets 1005-b, 1005-c, and can be used to start the turbinegenerators. In an alternative embodiment, black start generator 1003 canbe connected to each generator set 1005-a, 1005-b, 1005-c. 1005-d, or toa single turbine. The black start generator 1003 can initially providepower to equipment operating at 480 V, which can then be handed off to asmall 480 V transformer (not shown) located on each generator set1005-a, 1005-b, 1005-c, 1005-d, once the generator sets 1005-a, 1005-b,1005-c, 1005-d are operational.

Also shown are 480 V, three-phase, 60 Hz power lines between thecompressors 1030-a, 1030-b, generator sets 1005-a, 1005-b, 1005-c,1005-d, and fuel gas filtration and heating units 1035-a, 1035-b,1035-c, 1035-d. The power lines can depict the normal flow path ofelectrical current between the components of the microgrid. A chillerunit 1040 is shown, which can be an option for boosting the output ofthe turbine generators of generator sets 1005-a. 1005-b, 1005-c, 1005-dto negate the need for a fourth turbine. However, a fourth turbine maybe required in some embodiments, or can be used in lieu of an air inletchiller unit in some embodiments.

Also depicted in the illustrated embodiment is power transmissionequipment, which can include switchgear “B+” units 1025-b-1, 1025-b-2,and 13.8 kV, three-phase, 60 Hz power cables. The switchgear “B+” units1025-b-1, 1025-b-2 can provide power to the 3,500 kVA, 13.8 kV to 600 Vstep-down transformers 1045-a, 1045-b, 1045-c, 1045-d, 1045-e, 1045-f,1045-g, 1045-h and auxiliary units 1050-a, 1050-b. The auxiliary units1050-a, 1050-b can contain a large 13.8 kV to 600 V transformer, and canperform motor control, switching, and further distribution of power toauxiliary equipment and smaller loads. Power cables operating at 600 V,three-phase, 60 Hz are depicted according to a normal current flow path.

The mini-substations 1055-a, 1055-b shown can also be part of thedistribution network, receiving power supplied by an auxiliary trailer,and having 120 V and 240 V, single-phase, 60 Hz plugs for power plantlights, heaters, or data vans. Mini-substations 1055-a, 1055-b can alsocontain 600 V, three-phase, 60 Hz connections as an extra hub to providepower to any extra equipment. Extra equipment can include, for example,water transfer pumps, wireline equipment, electric cranes, worktrailers, living quarters, emergency showers, sand equipment, or futureadditions to the fleet.

The orientations and positions of the equipment in example 900 are forgraphical purposes only to illustrate the flow of electricity andinterconnections. On a well site, the equipment may be placed in anyorder or configuration geographically, as long as the electricalschematic does not change.

The example methods of using two “B+” switchgear units to provide powertransmission and load sharing advantageously allows for load sharing,while still having the advantage of fewer cables and less equipment. Themethod of using two “B+” switchgear units enables operation of twoseparate grids for redundancy or a single load sharing grid forefficiency.

Illustrated in FIG. 11 is a block diagram showing an example 1100 ofswitchgear load sharing for multiple generator sets 1105-a, 1105-b,1105-c, 1105-d, 1105-e, 1105-f, according to an embodiment. Here aswitchgear “C+” 1125-c is depicted having tie breakers 1109-a, 1109-bfor load sharing without provisions for an auxiliary trailer. In someexamples, the switchgear “C+” 1125-c trailer and switchgear “B+”1125-b-1, 1125-b-2 trailers can be interchanged with each other, as someapplications may not require auxiliary trailers or their correspondingequipment. Additionally, although three or four turbines are illustratedin many of the examples provided herein, this is not a limitation andalternate configurations having more or fewer turbines are envisioned toprovide power for multiple fleets or well sites, including non-hydraulicfracturing applications.

Similarly to FIGS. 8 and 9, the power transmission network can be brokeninto multiple banks with direct communication between generator sets1105-a, 1105-b and switchgear “B+” 1125-b-1 in the first bank 1107-a;generator sets 1105-c, 1105-d and switchgear “C+” 1125-c in the secondbank 1107-b; and generator sets 1105-e, 1105-f and switchgear “B+”1125-b-2 in the third bank 1107-c. Generator sets 1105-a, 1105-b can beload sharing through switchgear “B+” 1125-b-1, generator sets 1105-c,1105-d can be load sharing through switchgear “C+” 1125-c, and generatorsets 1105-e, 1105-f can be load sharing through another switchgear “B+”1125-b-2. Additionally, as in FIG. 9, the switchgear units “B+”1125-b-1, 1125-b-2 and switchgear “C+” 1125-c are able to load sharewith one another via tie breakers 1109-a, 1109-b.

FIG. 12 is a block diagram depicting an example 1200 of a switchgearload sharing option for providing power to equipment which is on adifferent site than the power generation equipment, according to anembodiment. Although illustrated in example 1200 in one configuration,many other switchgear configurations can provide power to equipmentlocated remotely from the power generation equipment.

As shown, a series of four generator sets 1205-a, 1205-b. 1205-c, 1205-dcan provide power to switchgear “A” 1225-a-1 at a first location. Powerreceived at switchgear “A” 1225-a-1 can be communicated to switchgear“A” 1225-a-2 at a second location. In the illustrated embodiment, loadsharing is handled by switchgear units “A” 1225-a-1, 1225-a-2, such thata tie breaker between two switchgear “B” units 1225-b-1, 1225-b-2 maynot be necessary. In one example, the long distance transmission linecan be several miles long and can be in the form of overhead or buriedpower lines. Any distance up to approximately 30 miles is feasible; atfurther distances, step-up transformers may be used to preventtransmission losses from becoming prohibitive. This approximation candepend on the power generated, the power required, and the powerconductors used.

Switchgear “A” 1225-a-2 can supply electrical power to two otherswitchgear units. Switchgear “B” 1225-b-1 can receive power fromswitchgear “A” 1225-a-2 and distribute the power to an auxiliary unitand one or more transformers as shown. Switchgear “B” 1225-b-2 can alsoreceive power from switchgear “A” 1225-a-2 and can distribute the powerto an auxiliary unit and one or more transformers.

FIG. 13 is a block diagram illustrating an example 1300 of a systemthat, like the system of FIG. 12, is capable of powering and loadsharing from multiple sites and processes, according to an embodiment.Generator sets 1305-a, 1305-b, 1305-c and switchgear “A+” 1325-a-1 canmake up a first bank 1307-a, and generator sets 1305-d, 1305-e. 1305-fand switchgear “A+” 1325-a-2 can make up a second bank 1307-b. In theillustrated example 1300, switchgear units “A+” 1325-a-1, 1325-a-2 areable to load share with one another. The switchgear units in thisconfiguration can provide load sharing through their internal electricalbus as well as through external power connections with tie breakers aspreviously described. Example cables are shown spanning between the twoswitchgear units “A+” 1325-a-1, 1325-a-2, which optionally are 13.8 kVcables for a tie breaker 1309. Tie breaker 1309 can allow for completeload sharing between all six turbines in generator sets 1305-a, 1305-b.1305-c, 1305-d, 1305-e, 1305-f.

Each switchgear “C” 1325-c-1, 1325-c-2 can be used to power sites likedrilling rigs, compressor stations, nitrogen plants, “man camps,”pumping stations, a second fracturing site (e.g., for pump-downoperations, injections tests, low rate jobs, or to power third partyequipment), etc. The switchgear units “B” 1325-b-1, 1325-b-2 combinedcan power a single hydraulic fracturing fleet. As previously described,the lines from switchgear units “A+” 1325-a-1, 1325-a-2 to switchgearunits “C” 1325-c-1, 1325-c-2 and switchgear units “B” 1325-b-1, 1325-b-2can be representative of power transmission lines and can be as long as30 miles in this configuration. The lines from switchgear units “C”1325-c-1, 1325-c-2 and switchgear units “B” 1325-b-1, 1325-b-2 can berepresentative of diesel locomotive cables (“DLO”) which, when laid outon the ground between the equipment, may span about one mile indistance. In other embodiments the distances can be about 25 feet toabout 200 feet. Buried or suspended cables can also be used if desiredor required.

FIG. 14 illustrates an example 1400 of a configuration for load sharingwith a utility grid, according to an embodiment. In the illustratedexample, the power transmission network is broken into two banks withdirect communication between generator sets 1405-a, 1405-b andswitchgear “B+” 1425-b in the first bank 1407-a, and generator sets1405-c. 1405-d and switchgear “C+” 1425-c in the second bank 1407-b. Inalternate embodiments, generator sets 1405-c, 1405-d can optionally beexcluded.

In an example of operation, the transformer 1445 can convert the gridvoltage to the power generation voltage, and tie breakers 1409-a, 1409-bcan enable the switchgear units “B+” 1425-b and “C+” 1425-c to loadshare between the generator sets 1405-a, 1405-b, 1405-c. 1405-d and theutility grid. For example, if the utility grid is transmitting power at69 kV, the transformer 1445 can step down the 69 kV voltage to 13.8 kVfor use by the microgrid. In this configuration, power can be eitherprovided to the grid or supplemented from the utility grid during timesof peak power demand.

Depicted in FIG. 15 is another example 1500 for load sharing with autility grid, according to an embodiment. Multiple transformers 1545-a,1545-b are shown to depict the replacement of generator sets (e.g.,generator sets 1405-c, 1405-d as illustrated in the embodiment shown inFIG. 14) with grid power. In the illustrated embodiment, multiple cablescan be used to share the power load to allow for smaller cable sizes andtransformers. In this embodiment, switchgear “A+” 1525-a can be used forload sharing, and tie breakers 1509-a, 1509-b can be located at eachconnection point with utility grid on switchgear “A+” 1525-a. Switchgear“A+” 1525-a can also supply electrical power to two other switchgear “B”units 1525-b-1, 1525-b-2.

In some embodiments, a small, diesel-fueled piston engine generator (notshown) can be used in lieu of an extra turbine generator for providingelectrical power to transmission and distribution systems, which can addan extra megawatt of power if peak demand cannot be met with theexisting turbine generators. An inability to meet peak demand could bedue to hot weather, turbine de-rate, long transmission distance, orextra power demand from a user. These systems of switchgear load sharingby using either tie breakers or a hierarchy of switchgear unitssupplying power to each other can be used with any method of powergeneration. Power generation can be provided from turbine generators,piston engine generators, rotary engine generators, solar power cells,wind turbine power, utility grid power, or any other method ofelectricity generation. Switchgear trailers can be positioned on mobiletrailers in some embodiments, or can be body-load or skid mounted unitsin other embodiments.

Examples of microgrid designs use 13.8 kV for transmission stepped downto 600 V for equipment, and in some cases 480 V for distribution toequipment. It is possible to use different voltages and to design orrefit the switchgear trailers accordingly. The principles of power loadsharing, transmission, and distribution can remain the same regardlessof the generated voltage. Voltage levels such as 138 kV, 69 kV, 50 kV,12 kV, 4,160 V, 1,380 V, 600 V, or 480 V can be used for transmission orpower distribution. These voltages are based on a small sample of themany common methods used in the national power grids; technically, anyvoltage can be specified and used.

The type of power conductor used can be dependent on the currentequipment requirements, customer requirements, and method of powertransmission and distribution. In one embodiment, power transmissionbetween generator sets and switchgear units employs a single large cableper connection, each cable containing conductors for all three powerphases, ground, and ground check. Power distribution betweentransformers and fracturing equipment can include diesel locomotive(DLO) cable, which can lie on the ground between the equipment. Twocables can be used for each power phase, totaling six power cables(three-phase power, with two cables per phase). This practice allowscables to be smaller, lighter, and easier to manage. Also an equipmentground spanning between the transformers and equipment can be used,which in one example can bring the power cable requirement to sevensingle conductor DLO cables per fracturing pump. However, many possiblecable configurations exist. In some embodiments a single cable per phasecan be used, or three or more cables per phase can also be used. Themethod of using multiple single-conductor cables can also be used for13.8 kV transmission between switchgear units.

It is also possible to use multi-conductor cables for 600 V powerdistribution; these cables can be similar to those used for 13.8 kVtransmission, and can contain all three phases and a ground inside thecable. A single multi-conductor cable can be used in some embodiments,or several multi-conductor cables can be used to split the power load sothat the cable can be lighter and smaller in other embodiments. Thesemulti-conductor cables can have an internal ground and ground check insome embodiments, or the grounds can be external in other embodiments.These power cables can simply lie on the ground in between theequipment. The cables can also be suspended like power transmissionlines, in which case non-insulated cables could be used. Alternativelythe cables can also be buried underground to be out of sight and toavoid trip hazards.

The present disclosure described herein, therefore, is well adapted tocarry out the objects and attain the ends and advantages mentioned, aswell as others inherent therein. While a presently preferred embodimentof the disclosure has been given for purposes of disclosure, numerouschanges exist in the details of procedures for accomplishing the desiredresults. These and other similar modifications will readily suggestthemselves to those skilled in the art, and are intended to beencompassed within the spirit of the present disclosure disclosed hereinand the scope of the appended claims.

What is claimed is:
 1. A hydraulic fracturing system for fracturing asubterranean formation comprising: a plurality of electric pumps fluidlyconnected to a well associated with the subterranean formation andpowered by at least one electric motor, and configured to pump fluidinto a wellbore associated with the well; two electrical banks, each ofthe two electrical banks comprising: a generator electrically coupled tothe plurality of electric pumps, and a switchgear electrically coupledto the generator and configured to distribute an electrical load betweenthe plurality of electric pumps and the generator; a tie breakerelectrically coupled between respective switchgears of the twoelectrical banks, the tie breaker distributing the electrical loadresponsive to a position of the tie breaker; a transformer electricallycoupled to a utility grid; and a second tie breaker electrically coupledbetween at least one switchgear of the two electrical banks and thetransformer.
 2. The hydraulic fracturing system of claim 1, wherein eachof the two electrical banks is configured to distribute the electricalload between the plurality of electric pumps and the respectivegenerators associated with the two electrical banks independent of anoperating status of other electrical banks of the two electrical banks.3. The hydraulic fracturing system of claim 1, wherein the systemcomprising the plurality of electric pumps, the generator, and theswitchgear comprises a single electrical microgrid.
 4. The hydraulicfracturing system of claim 1, wherein the tie breaker is configured to:evenly distribute the electrical load between the plurality of electricpumps and generators of the two electrical banks when the tie breaker isin a closed position; and isolate one or more of the plurality ofelectric pumps and at least one electrical bank when the tie breaker isin an open position.
 5. The hydraulic fracturing system of claim 1,wherein each electrical bank of the two electrical banks furthercomprises respective second generators, wherein: the tie breaker is inthe closed position; both generators of one electrical bank of the twoelectrical banks are operational; and the second generator of the otherelectrical bank of the two electrical banks is shut down while thegenerator is active; wherein the electrical load is evenly distributedamong the generators of the one electrical bank and the generator of theother electrical bank.
 6. The hydraulic fracturing system of claim 1,further comprising: a third electrical bank comprising a generator and aswitchgear; and a second tie breaker electrically coupled between atleast one switchgear of the two electrical banks, the second tie breakerdistributing the electrical load responsive to a position of the secondtie breaker.
 7. The hydraulic fracturing system of claim 1, wherein atleast one of the switchgears is configured to distribute power among anyof one or more transformers, auxiliaries, other switchgear units, or acombination thereof.
 8. The hydraulic fracturing system of claim 7,wherein the auxiliaries comprise one or more of any of a blender,electric wireline equipment, a water transfer pump, an electric crane, adata van, a work trailer, living quarters, an emergency shower, sandequipment, a turbine inlet chiller, a compressor station, a pumpingstation, a second fracturing site, a drill rig, or a nitrogen plant, ora combination thereof.
 9. The hydraulic fracturing system of claim 1,further comprising: an electrical connection between a utility grid andat least one of the switchgears.
 10. The hydraulic fracturing system ofclaim 1, further comprising: a power connection panel associated withthe plurality of electric pumps, wherein the power connection panelcomprises: plurality of power connections for each of the plurality ofelectric pumps; and a system ground connection configured to act as aground between the plurality of electric pumps and a transformer,wherein the transformer is configured to provide power to the pluralityof electric pumps.
 11. The hydraulic fracturing system of claim 1,further comprising: a variable frequency drive connected to the at leastone electric motor to control the speed of the at least one electricmotor, wherein the variable frequency drive is adapted to performelectric motor diagnostics.
 12. A hydraulic fracturing system forfracturing a subterranean formation comprising: a plurality of electricpumps fluidly connected to a well associated with the subterraneanformation and powered by at least one electric motor, and configured topump fluid into a wellbore associated with the well; two electricalbanks, each of the two electrical banks comprising: a generatorelectrically coupled to the plurality of electric pumps, and aswitchgear electrically coupled to the generator and configured todistribute an electrical load between the plurality of electric pumpsand the generator; a tie breaker electrically coupled between respectiveswitchgears of the two electrical banks, the tie breaker distributingthe electrical load responsive to a position of the tie breaker; and avariable frequency drive connected to the at least one electric motor tocontrol the speed of the at least one electric motor, wherein thevariable frequency drive is adapted to perform electric motordiagnostics.
 13. The hydraulic fracturing system of claim 12, whereineach of the two electrical banks is configured to distribute theelectrical load between the plurality of electric pumps and therespective generators associated with the two electrical banksindependent of an operating status of other electrical bank of the twoelectrical banks.
 14. The hydraulic fracturing system of claim 12,wherein the system comprising the plurality of electric pumps, thegenerator, and the switchgear comprises a single electrical microgrid.15. The hydraulic fracturing system of claim 12, wherein the tie breakeris configured to: evenly distribute the electrical load between theplurality of electric pumps and generators of the two electrical bankswhen the tie breaker is in a closed position; and isolate one or more ofthe plurality of electric pumps and at least one electrical bank whenthe tie breaker is in an open position.
 16. The hydraulic fracturingsystem of claim 12, wherein each electrical bank of the two electricalbanks further comprises respective second generators, wherein: the tiebreaker is in the closed position; both generators of one electricalbank of the two electrical banks are operational; and the secondgenerator of the other electrical bank of the two electrical banks isshut down while the generator is active; wherein the electrical load isevenly distributed among the generators of the one electrical bank andthe generator of the other electrical bank.
 17. The hydraulic fracturingsystem of claim 12, further comprising: a third electrical bankcomprising a generator and a switchgear; and a second tie breakerelectrically coupled between at least one switchgear of the twoelectrical banks, the second tie breaker distributing the electricalload responsive to a position of the second tie breaker.
 18. Thehydraulic fracturing system of claim 12, wherein at least one of theswitchgears is configured to distribute power among any of one or moretransformers, auxiliaries, or other switchgear units, or a combinationthereof.
 19. The hydraulic fracturing system of claim 12, furthercomprising: a transformer electrically coupled to a utility grid; and asecond tie breaker electrically coupled between at least one switchgearof the two electrical banks and the transformer.